1. Field of the Invention
The present invention is in the field of apparatus and methods for treating food products with ozone, primarily for the purpose of sterilization.
2. Description of the Prior Art
Ozone gas (O.sub.3) is a very strong oxidizing agent, having an oxidation potential more than twice that of chlorine and approximately three times that of hydrogen peroxide. Ozone also has the advantage of breaking down upon use as an oxidant into oxygen (O.sub.2), which is normally beneficial. Thus, ozone currently finds widespread usage as an oxidizing agent for bacterial, virus, and mold control for meat and fish storage, fresh fish processing for greater transportation range in the "fresh" state, meat, fish and poultry markets, produce storage, restaurants, cooliing towers, animal feed products, marine life, architectural lakes, beverage plants, swimming pools, potable water systems, and tertiary waste systems. Ozone is also currently widely used for odor control in air conditioning systems, industrial plants, restaurants, mortuaries, rest homes, pet shops, animal hospitals, restrooms, and hotels. Applicant is aware of a current use of ozone to extend the period of time that fresh fish will remain sufficiently fresh for marketing, which has recently enabled Alaskan fish to be shipped to the 48 contiguous states and distributed therein as "fresh" fish.
While the use of ozone in connection with food products is primarily for sterilization, it is also useful for preservation of some food products. For example, the treatment of raw onions with ozone will inhibit the growth of green sprouts. Also, ozone treatment will retard the ripening of bananas.
All current usages of ozone for the sterilization or preservation of food products of which applicant is aware are strictly on a "batch" basis, where the food is placed in a container, which may be a room, and the container is flooded with ozone for an appropriate period of time. Such batch treatment of food products with ozone is not practical for high production items, and it is also very wasteful of ozone because all or most of the ozone used for a particular batch is lost when the room or other container is opened and a treated batch is removed and replaced by an untreated batch.
Because of these problems with the batch ozone treatment of food products, there has long been a need in the art for a continuous process system for treating food products capable of processing the food products at a high production rate while at the same time preserving in the system all or most of the ozone that has not broken down to oxygen. While there is some prior patent art disclosing continuous process ozone food treatment systems, these have had the serious deficiencies of (1) applying the ozone in such a highly diluted state that the treatment could not be fully effective, (2) not being capable of containing and preserving the unreacted ozone, and therefore requiring use of an undesirably large amount of ozone for the amount of sterilization accomplished, or (3) transported or otherwise handled the food products in such a way that only such durable food products as grains could be processed, and fragile food products such as potato chips, dehydrated onions and other vegetables, leafy-type vegetables, and fragile fruits such as grapes, could not possibly be processed without severe damage.
Referring to the prior patent art, a batch food treatment system is seen in U.S. Pat. No. 680,630 to Williams et al., which disclosed ozone treatment of fish on a batch basis. The system of this disclosure not only had the disadvantages inherent in a batch system of ozone loss when the storage house was opened for removal and replacement of treated products and limited production capability, but also this patent taught that only a small portion of the flow of air to the treatment house was to be ozone, and the ozone that was used was already only a small fraction of the air from which it was prepared because it was prepared by means of an electric discharge.
Typical of the prior art patent disclosures of continuous process systems for treating food products with ozone are the Heyde etal. U.S. Pat. No. 765,972, Wiliams Reissue U.S. Pat. No. 13,064, Eolkin U.S. Pat. No. 3,341,280, and Darrah U.S. Pat. No. 2,108,030. The Heyde et al., Williams, and Eolkin patents were all limited to the treatment of grain products, and the systems disclosed therein would have been highly damaging to fragile food products. Heyde et al. disclosed the continuous process treatment of ground wheat. Ozone was applied to the wheat in a mixer that would act like a grinder for such delicate food products as dried onions or potato chips. The ozone in Heyde et al. was produced by an electric discharge through air, so it would be only a minor fraction of air supplied to the ground wheat in the mixer. The treated product left the mixer out of a conduit in the bottom, so that ozone would be freely lost from the system by the effects of gravity. Williams disclosed the oxidizing of flour with electrolytically separated oxygen from water, so there would only be a very small percentage of ozone in this treatment. The oxidation occurred in a screw-type feeder, so the apparatus could not be used for fragile food materials. The Eolkin patent disclosed a continuous process system only applicable to fine particulate food products such as spices, the system working on a "fluidizing" principle in which the particles flowed with the ozone or other sterilizing gas. Eolkin is the only patent of which applicant is aware where there was any attempt to conserve the ozone or other sterilizing gas, but this was accomplished by utilizing auger-type feed mechanisms that were effectively plugged with the powdered food product so as to conserve the gas, and such auger-type devices would be severely damaging to delicate food products. The Darrah patent disclosed continuous processing of milk through a corona discharge that would produce ozone, but only as a minor fraction of air applied to the milk. The Darrah system was applicable only to a liquid product, and could not be used for solid food products.
Di Giacinto et al. U.S. Pat. No. 2,635,051 disclosed a conveyor system for ozone treatment of boxed mushrooms. This system was not applicable to uncontained fragile vegetables or other food products, and the boxes were conveyed in a wide open region under where the ozone was produced, so the ozone was freely lost from the system and had to be continuously replaced. The ozone was produced by radiation lamps, so it would have been only a minor fraction of air applied to the boxed mushrooms. Another problem with the Di Giacinto et al. system was that confinement of the mushrooms in the boxes would have seriously interfered with the free application of ozone to the mushrooms packed together in the boxes.
The Rivkowich U.S. Pat. No. 3,809,769 disclosed the use of hydrogen peroxide or ozone on spent tea to increase the yield in making instant tea, so this patent disclosure was for a purpose different than sterilization of food products. The Visness et al. U.S. Pat. No. 3,203,809 dealt with the smoking of meat, and utilized a corona discharge to cause uniform ionization, and hence precipitation, of the smoke. While a small fraction of ozone would be incidentally produced in the air, that would be freely lost from the system. The Rhodes U.S. Pat. No. 4,072,762 related to controlling steam during the baking of bread by use of an electrostatic field. If ozone were incidentally produced by such electrostatic field, which is questionable, it would be a very minor amount, and it would have been free to flow out of the baking oven.